The same way we used Jupiter to find the constellation Scorpius a few weeks back, we can use Saturn to find Sagittarius the Archer. Better known as the Teapot from its shape, the constellation never gets very high in the sky viewed from the northern United States and Canada. For me, the bottom half of the Teapot doesn’t rise above the trees until it’s due south and highest in the sky. But after Orion, Ursa Major and a few others, Sagittarius remains one of my favorite constellations not only for its shape but also because there are a lot of wonderful things to look at here in binoculars or a telescope.
Sagittarius is also home to a bright section of the Milky Way and the center of the galaxy itself. To find it, face south around 10:30 p.m. in late July. The first thing you’ll see is the brilliant planet Jupiter about a third of the way up in the sky. Now, reach out a balled fist and put Jupiter at one end and look three fists to the left and below. You should see another bright “star” — that’s Saturn.
Once you’ve got Saturn in view, reach your hand out at arm’s length, but this time look three fingers (held together) below the planet and you should see a small trapezoid of stars. If you include the star just above and to the right of the figure, you’ll see it forms a little dipper. In fact, it’s an asterism or star-pattern nicknamed the Milk Dipper. That name comes from the shape and its location not far from the band of the Milky Way.
Pictured another way, it forms the handle and top of the Teapot. With the Milk Dipper under your belt, direct your gaze below and right of Teapot top to find the triangular “spout,” then connect spout and dipper to complete the pot’s outline. Sagittarius’ second brightest star Nunki (NOON-kee) shines from the top of the handle. The name is an ancient one, harkening back to the Babylonians to whom NUN-KI referred to a group of stars representing their sacred city of Eridu on the Euphrates River. Later, the name was applied exclusively to this particular star in the constellation.
Notice that the Milky Way flows over the top of the Teapot and past its spout. Because the band is low in the sky from mid-northern latitudes skywatchers in the northern half of the U.S. and much of Europe its light — and gloriousness — is often absorbed by haze. Here again is another excuse for traveling to the Caribbean or the southern hemisphere. The better to see the Sagittarius Milky Way!
When you face the Teapot you’re looking toward the center of the Milky Way galaxy 26,000 light years away. Billions of stars and a host of cosmic dust clouds lie between us and the core. The stars pile up to form the thick ribbon of hazy light — the band of the Milky Way — while the dust blocks the light of distant stars, creating dappled patches of darkness (see photo above) within the band. We see a dense band of stars instead of random stars all over the sky because our solar system is located within the Frisbee-like disk of the galaxy. When we look through the Frisbee — along its plane where the stars are concentrated — the stars pile into a hazy braid. When we look outside that band, the stars thin out rapidly.
The very center of the galaxy, shown by the red dot in the diagram above, sits just off the spout. It would shine with great brilliance were it not for intervening dust. Astronomers using radio and infrared telescopes have literally peeled back the dusty curtain and discovered what lies at the core — a supermassive black hole with a mass equal to 4 million of our suns and a diameter of 14.6 million miles. Many larger galaxies like our own have massive black holes in their cores.
In a future installment we’ll explore some of Sagittarius’s many bright nebulae and clusters visible in nothing more than a pair of binoculars. For now, head out the next clear night and get familiar with the constellation. Remember it’s low in the sky for many of us, so try to find a place with a good view to the south.